The present invention relates to hermetic compressors and more particularly to two stage rotary compressors using carbon dioxide as the working fluid.
Conventionally, multi-stage compressors are ones in which the compression of the refrigerant fluid from a low, suction pressure to a high, discharge pressure is accomplished in more than one compression process. The types of refrigerant generally used in refrigeration and air conditioning equipment include chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). Additionally, carbon dioxide may be used as the working fluid in refrigeration and air conditioning systems. By using carbon dioxide refrigerant, ozone depletion and global warming are nearly eliminated. Carbon dioxide is non-toxic, non-flammable, and has better heat transfer properties than CFCs and HCFCs, for example. The cost of carbon dioxide is significantly less than CFC and HCFC. Additionally, it is not necessary to recover or recycle carbon dioxide, which contributes to significant cost savings in training and equipment.
In a two-stage compressor, the suction pressure gas is first compressed to an intermediate pressure. The intermediate pressure gas is then generally collected in an accumulator. From the accumulator, the intermediate pressure gas is drawn into a second compressor mechanism where it is compressed to a higher, discharge pressure for use in the remainder of the refrigeration system.
The compression mechanisms of the two-stage compressor may be in one of two orientations. The compression mechanisms may be stacked adjacent one another on one side of the motor, or positioned with one compression mechanism located on opposite sides of the motor. Typically, the compression mechanisms are mounted on the compressor drive shaft for rotation therewith. As the drive shaft rotates to drive the compression mechanisms, an oil pump mounted at the end of the shaft is actuated. The oil pump is provided to draw lubricant from an oil sump in the compressor housing into a longitudinal bore in the drive shaft and deliver the lubricant to bearing surfaces in the compressor.
The oil pump is generally mounted on the end of the drive shaft. In a substantially vertical compressor, the oil pump may be at least partially immersed in the oil sump. In a substantially horizontal compressor, the pump is conventionally provided with an oil pick up tube extending from the pump into the oil sump. The pump may be a rotary pump which includes a fixed casing housing gears, cams, screws, vanes, plungers, or the like with close tolerances between the internal component and the pump casing. The internal components of the rotary pump are generally mounted directly on the drive shaft for rotation therewith. As the drive shaft rotates, oil is drawn from the oil sump, through the oil pick up tube, and into the drive shaft.
A problem with having the oil pump mounted on the end of the drive shaft is that the length of the housing has to be increased to accommodate the pump, thus increasing the overall size of the compressor. Further, startup friction is much greater than operational friction due to the close tolerances between the internal components and the pump casing, which may increase the amount wear on the pump components.
It is desired to provide a hermetic rotary compressor with an improved lubrication system operable upon rotation of the rotor including a piston type pump which reduces pump wear and is mounted on the shaft in a position that allows the compressor housing to be shortened.
The present invention relates to an oil pump for a substantially horizontal, two-stage rotary compressor which uses carbon dioxide refrigerant as the working fluid. The rotary compressor has a non-rotating or stationary shaft with opposite ends thereof fixedly mounted to the compressor housing. A pair of rotary compression mechanisms are rotatably disposed about opposite ends of the stationary shaft and are fixed to one another via an interference fit between the compression mechanisms and the central bore of the compressor motor rotor.
The stationary shaft is provided with a longitudinal oil passage in fluid communication with an oil pump mounted to the stationary shaft. The oil pump includes a barrel extending into the oil sump and being integrally formed with a main body portion. Located at one end of the main body portion is an ear having a substantially circular opening therein in which the stationary shaft is received. A reciprocating piston is received in the barrel. Movement of the piston is effected through a ball located between the piston and a groove formed in the outer surface of an outboard bearing located adjacent the first stage compression mechanism. The outer surface of the outboard bearing is eccentric relative to the axis of rotation of the motor rotor. The eccentricity imparts cyclical downward movement to the piston against the force of a spring located between the lower end of the barrel and the end of the piston. The spring is provided to bias the ball into the outboard bearing groove.
Oil is received into the barrel through an inlet port. With the piston in an upward position, oil flows through the gap between the coils of the spring into an axial passage formed in the piston. The oil is forced into a discharge manifold formed in the main body portion as the piston moves downwardly. The oil then flows into the longitudinal bore in the stationary shaft to be distributed to the bearing surfaces of the compressor. A small portion of the oil is drawn further into the piston to lubricate interfacing surfaces between the ball and the outboard bearing.
The present invention provides a hermetic rotary compressor including a housing having an oil sump formed therein. A stationary shaft is fixedly mounted in the housing with a longitudinal bore formed in the shaft. A motor is mounted in the housing and has a rotor and a stator. The rotor has a first and a second end and is rotatably mounted on the shaft. A pair of compression mechanisms is rotatably mounted on the shaft. Each compression mechanism is rotatably couple to the rotor and lubricated with oil conducted through the longitudinal bore. Each compression mechanism has an outboard bearing rotatably mounted on the shaft. An oil pump is mounted on the stationary shaft and is operatively engaged with one of the outboard bearings. The oil pump is actuated by rotation of one of the outboard bearings and oil is pumped from the sump into the longitudinal bore by the oil pump.
The present invention also provides an oil pump for a hermetic rotary compressor having a rotatably mounted outboard bearing. The oil pump includes a barrel having a main body portion integrally formed therewith. The main body portion has an opening therein for mounting the oil pump. A reciprocating piston is received in the barrel and is operatively engaged with the outboard bearing such that rotation of the outboard bearing actuates the oil pump.
The present invention provides a method of pumping oil in a hermetic compressor to bearing surfaces in the compressor which includes: rotating a compression mechanism about a stationary shaft fixed within a compressor housing; moving a reciprocating piston in an oil pump located in the compressor housing in response to rotation of the compression mechanism about the stationary shaft; drawing oil from a sump located within the compressor housing into the oil pump through movement of the piston; forcing the oil in the oil pump into a longitudinal bore formed in the stationary shaft through movement of the piston; and distributing oil received from the pump by the longitudinal bore to bearing surfaces of the compression mechanism.
One advantage of the present invention is that the oil pump is moved from the end of the stationary shaft to a position closer to the compressor motor allowing the length of the compressor housing to be reduced.
A further advantage of the present invention is that with this type of oil pump, startup friction is not much greater than operational friction, which minimizes that amount of wear on the pump components.